Metabolic identification of carnitine biomarkers for the differential diagnosis of uterine disorders in bitches.

Recent studies have improved the understanding of uterine disorders in bitches, but accurate differential diagnosis remains challenging, particularly between degenerative conditions, such as cystic endometrial hyperplasia (CEH)-mucometra, and inflammatory/infectious disorders, as endometritis and pyometra. Because clinical and imaging findings often lack histopathological precision, this study aimed to identify in situ metabolic biomarkers for more accurate differentiation among CEH-Mucometra, endometritis, and pyometra. Thirty-nine bitches aged 2-13 years underwent elective or therapeutic ovariohysterectomy and were classified by uterine histology into CEH-Mucometra (n = 10), Endometritis (n = 10), Pyometra (n = 10), and Control/Diestrus (n = 9) groups. Endometrial fragments were subjected to targeted metabolomic analysis of 32 carnitines using LC-MS/MS with a 3200 QTRAP spectrometer and MarkerView 1.2.1 software. Orthogonal contrasts evaluated uterine disorders, lesion type, and differences between endometritis and pyometra. Statistical comparisons included Diestrus vs. diseased groups, CEH-Mucometra vs. inflammatory groups, and Endometritis vs. Pyometra, at P < 0.05. Of the 32 carnitines analyzed, 15 were quantified in at least one group, while 17 were undetected. Propionylcarnitine was lower in Mucometra than in inflammatory groups. Free carnitine, acetylcarnitine, propionylcarnitine, and butyrylcarnitine differed between Endometritis and Pyometra. Pyometra showed higher acetylcarnitine, malonylcarnitine/3-hydroxy-butyrylcarnitine, methylmalonyl/3-hydroxy-isovalerylcarnitine, and hexanoylcarnitine compared with CEH-Mucometra and Diestrus. Endometritis showed higher malonylcarnitine/3-hydroxy-butyrylcarnitine and methylmalonyl/3-hydroxy-isovalerylcarnitine than Mucometra. Notably, glutarylcarnitine/3-hydroxy-hexanoylcarnitine and 3-hydroxy-octadecenoylcarnitine were identified exclusively in Pyometra. Despite the inherent methodological limitations, it was concluded that canine endometrial carnitine metabolism varies according to the underlying uterine disorder. Thus, the uterine carnitine profile is promising for differential diagnosis, including two specific carnitine types differentially detected in the pyometra group.